1. Field of the Invention
This invention relates to a mounting structure of a surface acoustic wave filter adapted for use in a high frequency range.
2. Description of the Prior Art
A surface acoustic wave filter is making use of opposite piezoelectric effect that when electric field is applied to a resonator made of a piezoelectric material, the resonator is deformed to generate a distortion or stress. The surface acoustic wave filter abbreviated as a SAW filter has recently and widely been used in RF stage amplifiers and intermediate frequency amplifiers of TV receivers as well as in intermediate frequency amplifiers of FM Radio Receivers.
FIG. 1 shows a principle diagram of a such a SAW filter in which the reference numeral 1 denotes a SAW element. The reference numerals 2 and 3 as well as 4 and 5 designate opposed two pairs of electrodes of which the pair of electrodes 2 and 3, for example, are used as input electrodes while the other pair of electrodes 4 and 5 are used as output electrodes with surface acoustic wave being propagated as shown by arrows 6 from the input electrodes 2, 3 to the output electrodes 4, 5.
There electrodes are connected to outer circuits through two pairs of outgoing lines (not shown) connected to the electrodes 2, 3 and 4, 5 in parallel and four terminal pins.
However, in such a SAW filter, S-parameter of the SAW element itself largely varies in accordance with connecting condition between the outgoing lines (including bonding wires and terminal pins) and the outer circuits in a high frequency range higher than about 300 MHz. Particularly, the outgoing lines come to represent an intensive inductivity which causes radiation loss therefrom resulting in various operational troubles.